At the bottom of the Timeline view, click the menu button and select Show Volume.

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Select Sound > Show Volume Envelope

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In the Timeline view, right-click in the audio track area and select Show Volume.

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In the Sound toolbar, click the Show Volume Envelope button. You may need to add this button to the toolbar. Right-click the toolbar and select Customize.

A blue line, indicating the sound level, is displayed for each sound sequence.

Hold down the Alt key and click the line to add a new marker. A plus sign (+) on the cursor indicates that a keyframe will be added. You can add an unlimited number of volume keyframes.

Drag an existing marker to adjust the volume at a specific frame. When you drag a volume keyframe, the current dB level is displayed.

Hold the Alt key and click an existing volume keyframe to delete it. A minus sign (-) on the cursor indicates that the marker will be deleted.

The slope of the line indicates how quickly the sound changes from one level to another. If the slope is steep, the change is abrupt. If the slope is less inclined, the volume changes at a more gradual rate.